In CategoryTheory, the universal supertype--the type which all other types are (directly or indirectly) a subtype of.  Present in most languages; where it goes by names such as Object (many OO languages), GENERAL (EiffelLanguage), "t" (LispLanguage).  TheThirdManifesto refers to it as the greek letter alpha.

In many languages, TopType is abstract--there are no elements of TopType which are not elements of some other (declared) type; though this isn't true in Lisp and JavaLanguage ("new Object" is perfectly legal Java).
      
''Symbol: http://www.jfsowa.com/@top.gif ''

See also UniversalSet and SemanticSubtyping.

Compare with BottomType. ''Not to be confused with BottomMind''